In the field of mobile radio telephony, understood by the term “roaming” is the operation of a mobile communication terminal, for example a mobile radio telephone or a portable computer with corresponding mobile radio components, outside the home network. Roaming is used for instance between different GSM networks (Global System for Mobile Communication) or UMTS networks (Universal Mobile Telephone System), but also between mobile radio networks which work according to different standards. To enable the direct roaming of a subscriber between two mobile radio networks, roaming agreements have to be concluded between the respective operators of the mobile radio networks. In a visited mobile radio network (Visited Public Mobile Network, VPMN), a subscriber is registered in a visitor register (Visitor Location Register, VLR) using his subscriber identification (International Mobile Subscriber Identity, IMSI) from the number range of his home mobile radio network (Home Public Mobile Network, HPMN), and his location is stored in a home register (Home Location Register, HLR) of the home mobile radio network, i.e. a so-called location update is carried out.
Described in the patent application WO 98/10614 is a telecommunication method for indirect roaming enabling a subscriber of a home mobile radio network to connect to a visited mobile radio network without a roaming agreement with the home mobile radio network, the connection being achieved through means, for example a subscriber identification (IMSI) and a call number (MSISDN=Mobile Subscriber Integrated Services Digital Network), which are made available by a partner network having a roaming agreement, on the one hand, with the home mobile radio network and, on the other hand, with the visited mobile radio network.
In the method described in WO 98/10614, each identification module of the subscriber of the home mobile radio network contains two permanently stored subscriber identifications. A different call number is assigned to each subscriber identification. The first subscriber identification belongs to the number range of the home mobile radio network, the second to the number range of the partner network. In order to register in a visited network that does not have any roaming agreement with the home mobile radio network, the subscriber can deactivate the first subscriber identification from the home mobile radio network and activate the second subscriber identification from the partner network, and is thereby regarded in the visited network as a subscriber of the partner network; thus a roaming process for the visited network can be carried out via the partner network.
Since in the method according to WO 98/10614 each subscriber identification is assigned another, different call number, the calls with the first number for the subscriber have to be redirected with a complex and time-consuming mechanism. Subscriber-specific data, for example redirections of calls, additional numbers, etc. are moreover assigned to the subscriber identification in a completely conventional way and are thus only available in the home mobile radio network or in visited mobile radio networks having a roaming agreement with the home mobile radio network.
Described in the patent publication EP 0 990 364 is a telecommunication method for indirect roaming similar to that in WO 98/10614. According to EP 0 990 364, however, a common call number is assigned to the first subscriber identification of the home mobile radio network and to the second subscriber identification of the partner network.
Both the conventional standardized method for direct roaming as well as the above-described method for indirect roaming have the disadvantage that the subscriber is logged into the visited mobile radio network as a foreign subscriber and has to pay significantly higher connection fees than a local subscriber. Additional costs can also arise in particular when two subscribers from the same home mobile radio network who are located in a common visited mobile radio network communicate with each other and the connection thereby is generated via the home mobile radio network.